<!doctype html>
<meta charset="UTF-8">
<title>CSS Test Reference</title>
<style>
  .list-item {
    margin-left: 40px;
  }
</style>
<div class="list-item">
  [1] A1
  <div class="list-item">[1] B1</div>
  <div class="list-item">[2] B2</div>
</div>
<div class="list-item">[2] A2</div>
<div class="list-item">[3] A3</div>
